In a known method of making wear resistant lining, which is disclosed in U.S. Pat. No. 3,900,188, a screw extruder is provided with a wearing barrel which is inserted into a cavity in the extruder housing. The barrel is fixed there temporarily in the desired position, and the interstice between the external wall of the wearing barrel and the internal wall of the cavity is filled in with a castable material, the melting point of which is lower than the melting point of the wearing barrel material and than the melting point of the extruder housing material.
It is likewise already known, and generally customary in practice, to shrink-fit wearing barrels into the cavities of the extruder housings. This known method suffers from the following disadvantages: Both the internal wall of the cavity in the extruder housing and the external wall of the wearing barrel must be machined to an exact shrinkage dimension. The geometry of the oval or figure-of-eight shaped surfaces of the wearing barrel and of the cavity necessitates a large outlay of time, special machines and special measuring techniques for these machining operations. During the shrinking process the actual thermal expansions are variable with respect to the horizontal and vertical dimensions in the cross-sectional plane of the extruder housing. This results in differential contractions when the extruder housing cools down, and hence a non-uniform contact of the external wall of the wearing barrel with the internal wall of the caviity of the extruder housing. Owing to the only partial contact of the contact surfaces, an unsatisfactory heat transfer results; furthermore, the strength of the component comprising the extruder housing as well as that of the wearing barrel, is disadvantageously influenced. In this case also a satisfactory sealing cannot be obtained between the wearing barrel and the extruder housing, so that, particularly when corrosive substances are processed, they can penetrate into the gap between the wearing barrel and the cavity and lead to corrosion phenomena there. For this reason a costly welding together of wearing barrel and extruder housing is necessary, but this again is only possible if the wearing barrel and the extruder housing consist of weldable materials. This leads to a restriction in the choice of materials, more particularly as regards the wearing barrels. This welding increases the difficulty of repairs, because in order to extract the wearing barrels from the extruder housing, the welded joints must first of all be eliminated and then be reworked subsequently on a fresh wearing barrel. This involves the risk of thermal distortion of the extruder housing.
These disadvantages which have been described are in fact eliminated by the method first described above; but in that case casting gaps are required between the external wall of the wearing barrel and the internal wall of the cavity which are larger than 1 millimeter, in order that the castable material can be cast in to fill the interstice completely. Such wide gaps, however, considerably reduce the strength of the component comprising the extruder housing and the wearing barrel.
It is therefore the underlying aim of the present invention to develop further the method of the type initially described so that by reducing the gap width required between wearing barrel and extruder housing, the strength of the overall component is increased.